Functional role of somatostatin receptors in neuroendocrine and immune cells

During the last decade the concept of a narrow communication between the im mune and classical neuroendocrine systems has been supported by cumulative evidence. One of the common links between the two systems is formed by the production of somatostatin (SS), the presence of SS receptors (SS-R) and th e functional effects of SS on both endocrine and immune cells. While in the endocrine system SS-R activation is coupled to mainly inhibitory effects, both inhibitory and stimulatory effects of SS have been demonstrated on the function of immune cells tie proliferation and secretion). Moreover, er in contrast to endocrine cells tie growth hormone (GH)-secreting pituitary ce lls) in which SS and its analogues inhibit GH secretion in the nanomolar ra nge in a dose-dependent manner achieving maximal inhibitory effects at high er concentrations, biphasic effects of SS are generally found on the functi on of immune cells with inhibition at low (nanomolar) concentrations and ab sence of an effect at higher (micromolar) concentrations. Neuroendocrine ce lls often express multiple SS-R subtypes, which may be linked to specific f unctions. Scarce information is available so far on the SS-R subtype expres sion pattern as well as on the second messenger systems linked to SS-R acti vation in human lymphoid cells. The recent development of novel SS-R subtyp e-selective SS analogues will be helpful in unravelling the functional role s of the individual SS-R subtypes in SS-R-expressing human neuroendocrine a nd immune cells.